This invention relates to a hearing aid system for the handicapped and more particularly to such a system for processing signals prior to application of the same to the ear of a user.
It is known that the frequency response of a normal ear is not flat. At the lower frequency range, the response falls off depending upon the level or intensity of the audio signal. This is true of the rate of fall-off as this also depends upon the intensity of the signal. Such aspects of a normal ear's response are evident when viewing the well known Fletcher-Munson curves.
In order to simulate normal hearing for use in hearing aids for the handicapped, one desires to approach the characteristics of the normal ear by incorporating compensating circuitry within such devices. In any event, it is extremely difficult to do and if attempted, would result in cumbersome and expensive aids which would be extremely difficult to design and build.
Most hearing aids conventionally available, employ a volume control to enable the user to adjust the volume of the device according to his preferences and in regard to the particular environmental situation. Such volume controls in the prior art devices vary the audio output of the hearing aid without substantially affecting the frequency response; which response is usually determined by suitable filters incorporated in the device.
The present invention concerns itself with a volume control which operates to vary the audio output of the hearing aid while further serving to control the frequency response of the device according to variation or control of the volume adjustment. In this manner, the frequency response of the aid is varied according to the volume control to attempt to match the frequency response of a normal ear.
The frequency control afforded corresponds to the levels of soft conversational speech as well as moderate and loud speech.
Thus, a user of this aid is able to adjust the volume control and hence, the frequency response according to the intensity of conversational speech as being either soft, moderate or loud.
It is also known that the slope of the frequency response characteristics is also a function of the patient's loudness contours and his own loudness growth and hence, the volume taper can accommodate for these particular characteristics.